825 research outputs found
A Simple Cooperative Diversity Method Based on Network Path Selection
Cooperative diversity has been recently proposed as a way to form virtual
antenna arrays that provide dramatic gains in slow fading wireless
environments. However most of the proposed solutions require distributed
space-time coding algorithms, the careful design of which is left for future
investigation if there is more than one cooperative relay. We propose a novel
scheme, that alleviates these problems and provides diversity gains on the
order of the number of relays in the network. Our scheme first selects the best
relay from a set of M available relays and then uses this best relay for
cooperation between the source and the destination. We develop and analyze a
distributed method to select the best relay that requires no topology
information and is based on local measurements of the instantaneous channel
conditions. This method also requires no explicit communication among the
relays. The success (or failure) to select the best available path depends on
the statistics of the wireless channel, and a methodology to evaluate
performance for any kind of wireless channel statistics, is provided.
Information theoretic analysis of outage probability shows that our scheme
achieves the same diversity-multiplexing tradeoff as achieved by more complex
protocols, where coordination and distributed space-time coding for M nodes is
required, such as those proposed in [7]. The simplicity of the technique,
allows for immediate implementation in existing radio hardware and its adoption
could provide for improved flexibility, reliability and efficiency in future 4G
wireless systems.Comment: To appear, IEEE JSAC, special issue on 4
Cooperative Cognitive Relaying Under Primary and Secondary Quality of Service Satisfaction
This paper proposes a new cooperative protocol which involves cooperation
between primary and secondary users. We consider a cognitive setting with one
primary user and multiple secondary users. The time resource is partitioned
into discrete time slots. Each time slot, a secondary user is scheduled for
transmission according to time division multiple access, and the remainder of
the secondary users, which we refer to as secondary relays, attempt to decode
the primary packet. Afterwards, the secondary relays employ cooperative
beamforming to forward the primary packet and to provide protection to the
secondary destination of the secondary source scheduled for transmission from
interference. We characterize the diversity-multiplexing tradeoff of the
primary source under the proposed protocol. We consider certain quality of
service for each user specified by its required throughput. The optimization
problem is stated under such condition. It is shown that the optimization
problem is linear and can be readily solved. We show that the sum of the
secondary required throughputs must be less than or equal to the probability of
correct packets reception.Comment: This paper was accepted in PIMRC 201
Spatial Interference Cancelation for Mobile Ad Hoc Networks: Perfect CSI
Interference between nodes directly limits the capacity of mobile ad hoc
networks. This paper focuses on spatial interference cancelation with perfect
channel state information (CSI), and analyzes the corresponding network
capacity. Specifically, by using multiple antennas, zero-forcing beamforming is
applied at each receiver for canceling the strongest interferers. Given spatial
interference cancelation, the network transmission capacity is analyzed in this
paper, which is defined as the maximum transmitting node density under
constraints on outage and the signal-to-interference-noise ratio. Assuming the
Poisson distribution for the locations of network nodes and spatially i.i.d.
Rayleigh fading channels, mathematical tools from stochastic geometry are
applied for deriving scaling laws for transmission capacity. Specifically, for
small target outage probability, transmission capacity is proved to increase
following a power law, where the exponent is the inverse of the size of antenna
array or larger depending on the pass loss exponent. As shown by simulations,
spatial interference cancelation increases transmission capacity by an order of
magnitude or more even if only one extra antenna is added to each node.Comment: 6 pages; submitted to IEEE Globecom 200
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